Gilbert de Murcia

Poly(ADP-ribosyl)ation is an immediate DNA-damage-dependent post-translational modification of histones and other nuclear proteins that contributes to the survival of injured proliferating cells. Poly(ADP-ribose) polymerases (PARPs) now constitute a large family of 18 proteins, encoded by different genes and displaying a conserved catalytic domain in which PARP-1 (113 kDa), the founding member, and PARP-2 (62 kDa) are so far the sole enzymes whose catalytic activity has been shown to be immediately stimulated by DNA strand breaks. A large repertoire of sequences encoding novel PARPs now extends considerably the field of poly(ADP-ribosyl)ation reactions to various aspects of the cell biology including cell proliferation and cell death. Some of these new members interact with each other, share common partners and common subcellular localizations suggesting possible fine tuning in the regulation of this post-translational modification of proteins. This review summarizes our present knowledge of this emerging superfamily, which might ultimately improve pharmacological strategies to enhance both antitumor efficacy and the treatment of a number of inflammatory and neurodegenerative disorders. A provisional nomenclature is proposed.

Poly(ADP-ribose) polymerase [PARP; NAD+ ADP-ribosyltransferase; NAD+: poly(adenosine-diphosphate-D-ribosyl)-acceptor ADP-D-ribosyltransferase, EC 2.4.2.30] is a zinc-finger DNA-binding protein that detects specifically DNA strand breaks generated by genotoxic agents. To determine its biological function, we have inactivated both alleles by gene targeting in mice. Treatment of PARP-/- mice either by the alkylating agent N-methyl-N-nitrosourea (MNU) or by gamma-irradiation revealed an extreme sensitivity and a high genomic instability to both agents. Following whole body gamma-irradiation (8 Gy) mutant mice died rapidly from acute radiation toxicity to the small intestine. Mice-derived PARP-/- cells displayed a high sensitivity to MNU exposure: a G2/M arrest in mouse embryonic fibroblasts and a rapid apoptotic response and a p53 accumulation were observed in splenocytes. Altogether these results demonstrate that PARP is a survival factor playing an essential and positive role during DNA damage recovery.

We have studied the apoptotic response of poly(ADP-ribose) polymerase (PARP)−/− cells to different inducers and the consequences of the expression of an uncleavable mutant of PARP on the apoptotic process. The absence of PARP drastically increases the sensitivity of primary bone marrow PARP−/− cells to apoptosis induced by an alkylating agent but not by a topoisomerase I inhibitor CPT-11 or by interleukin-3 removal. cDNA of wild type or of an uncleavable PARP mutant (D214A-PARP) has been introduced into PARP−/− fibroblasts, which were exposed to anti-CD95 or an alkylating agent to induce apoptosis. The expression of D214A-PARP results in a significant delay of cell death upon CD95 stimulation. Morphological analysis shows a retarded cell shrinkage and nuclear condensation. Upon treatment with an alkylating agent, expression of wild-type PARP cDNA into PARP-deficient mouse embryonic fibroblasts results in the restoration of the cell viability, and the D214A-PARP mutant had no further effect on cell recovery. In conclusion, PARP−/− cells are extremely sensitive to apoptosis induced by triggers (like alkylating agents), which activates the base excision repair pathway of DNA, and the cleavage of PARP during apoptosis facilitates cellular disassembly and ensures the completion and irreversibility of the process. We have studied the apoptotic response of poly(ADP-ribose) polymerase (PARP)−/− cells to different inducers and the consequences of the expression of an uncleavable mutant of PARP on the apoptotic process. The absence of PARP drastically increases the sensitivity of primary bone marrow PARP−/− cells to apoptosis induced by an alkylating agent but not by a topoisomerase I inhibitor CPT-11 or by interleukin-3 removal. cDNA of wild type or of an uncleavable PARP mutant (D214A-PARP) has been introduced into PARP−/− fibroblasts, which were exposed to anti-CD95 or an alkylating agent to induce apoptosis. The expression of D214A-PARP results in a significant delay of cell death upon CD95 stimulation. Morphological analysis shows a retarded cell shrinkage and nuclear condensation. Upon treatment with an alkylating agent, expression of wild-type PARP cDNA into PARP-deficient mouse embryonic fibroblasts results in the restoration of the cell viability, and the D214A-PARP mutant had no further effect on cell recovery. In conclusion, PARP−/− cells are extremely sensitive to apoptosis induced by triggers (like alkylating agents), which activates the base excision repair pathway of DNA, and the cleavage of PARP during apoptosis facilitates cellular disassembly and ensures the completion and irreversibility of the process. Apoptosis or programmed cell death is a fundamental biological process that plays an important role in early development, cell homeostasis, and in diseases such as neurodegenerative disorders and cancer (1Kerr J.F.R. Winterford C.M. Harmon B.V. Cancer. 1994; 73: 2013-2026Crossref PubMed Scopus (2167) Google Scholar, 2Kusiak J.W. Izzo J.A. Zhao B. Mol. Chem. Neuropathol. 1996; 28: 153-162Crossref PubMed Scopus (33) Google Scholar, 3Jacobson M.D. Weill M. Raff M.C. Cell. 1997; 88: 347-354Abstract Full Text Full Text PDF PubMed Scopus (2415) Google Scholar). Programmed cell death can occur in response to many stimuli such as genotoxic insult when DNA repair is saturated, removal of growth factors, or activation of the CD95 antigen by CD95 ligand or anti-CD95 antibodies. Morphologically it is characterized by the appearance of membrane blebbing, cell shrinkage, chromatin condensation, and DNA cleavage, and finally the cell is fragmented into membrane-bound apoptotic bodies. At the biochemical level, there is increasing evidence for a central role of the family of cysteine proteases, the caspases, in the pathway that mediates the highly ordered process leading to cell death (4Nicholson D. Thornberry N. Trends Biochem. Sci. 1997; 22: 299-306Abstract Full Text PDF PubMed Scopus (2187) Google Scholar). Caspases have been identified as the enzymes responsible for the proteolysis of key proteins to be selectively cleaved at the onset of apoptosis. It appears that the role of these proteases in cell suicide is to disable critical homeostatic and repair enzymes as well as key structural components. A discrete but increasing number of specific proteins appears to be targeted for proteolytic cleavage during apoptosis, including poly(ADP-ribose) polymerase (PARP, 1The abbreviations used are: PARP, poly(ADP-ribose) polymerase; MEF, mouse embryonic fibroblast; PBS, phosphate-buffered saline; MMS, N-methylmethanesulfonate; MNU, methylnitrosourea; wt, wild-type; X-gal, 5-bromo-4-chloro-3-indolyl β-d-galactopyranoside; BM, bone marrow; BER, base excision repair; GFP, green fluorescence protein. EC 2.4.2.30), which was first described in Ref. 5Lazebnik Y.A. Kaufmann S.H. Desnoyers S. Poirier G.G. Earnshaw W.C. Nature. 1994; 371: 346-347Crossref PubMed Scopus (2351) Google Scholar. In the last years, cleavage of PARP has been used extensively as a marker of apoptosis. However, the reason for the cell to inactivate this protein during the execution phase of apoptosis is not fully understood. PARP is a nuclear zinc finger DNA-binding protein that detects and binds to DNA strand breaks. PARP has a modular organization comprising a NH2-terminal DNA-binding domain, a central regulatory domain, and a COOH-terminal catalytic domain. At a site of DNA breakage, PARP catalyzes the transfer of the ADP-ribose moiety from its substrate, NAD+, to a limited number of protein acceptors (heteromodification) involved in chromatin architecture (histones H1 and H2B, lamin B) or in DNA metabolism (topoisomerases, DNA replication factors) including PARP itself (automodification) (6Althaus F.R. Richter C. Mol. Biol. Biochem. Biophys. 1987; 37: 1-237PubMed Google Scholar, 7de Murcia G. Ménissier-de Murcia J. Trends Biochem. Sci. 1994; 19: 172-176Abstract Full Text PDF PubMed Scopus (763) Google Scholar, 8Lautier D. Hoflack J.C. Kirkland J.B. Poirier D. Poirier G.G. Biochim. Biophys. Acta. 1994; 1221: 215-220Crossref PubMed Scopus (18) Google Scholar, 9Oei S. Griesenbeck J. Schweiger M. Rev. Physiol. Biochem. Pharmacol. 1997; 131: 4135-4137Google Scholar). Mice lacking PARP have been generated by homologous recombination to assess the biological consequences of PARP deficiency (10Wang Z.Q. Auer B. Stingl L. Berghammer H. Haidacher D. Schweiger M. Wagner E.W. Genes Dev. 1995; 9: 509-520Crossref PubMed Scopus (715) Google Scholar, 11Ménissier de Murcia J. Niedergang C. Trucco C. Ricoul M. Dutrillaux B. Mark M. Oliver F.J. Masson M. Dierich A. LeMeur M. Walztinger C. Chambon P. de Murcia G. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 7303-7307Crossref PubMed Scopus (968) Google Scholar, 12Wang Z.-Q. Stingl L. Morrison C. Jantsch M. Marek L. Schulze-Ostoff K. Wagner E. Genes Dev. 1997; 18: 2347-2358Crossref Scopus (517) Google Scholar). We have reported that PARP−/− mice are hypersensitive to genotoxic agents, like γ-rays and monofunctional alkylating agents, compared with their +/+ litter mates. Mutant mice displayed genomic instability as shown by an increased rate of sister chromatid exchanges and an increased occurrence of chromosomal breaks in their bone marrow cells. Using PARP−/− mice-derived cells, we and others have established that apoptosis occurs in the absence of PARP (11Ménissier de Murcia J. Niedergang C. Trucco C. Ricoul M. Dutrillaux B. Mark M. Oliver F.J. Masson M. Dierich A. LeMeur M. Walztinger C. Chambon P. de Murcia G. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 7303-7307Crossref PubMed Scopus (968) Google Scholar, 12Wang Z.-Q. Stingl L. Morrison C. Jantsch M. Marek L. Schulze-Ostoff K. Wagner E. Genes Dev. 1997; 18: 2347-2358Crossref Scopus (517) Google Scholar, 13Leist M. Single B. Künstle G. Volbracht C. Hentze H. Nicotera P. Biochem. Biophys. Res. Commun. 1997; 233: 518-522Crossref PubMed Scopus (135) Google Scholar). However, we have shown that PARP−/− splenocytes exposed to a monofunctional alkylating agent underwent much more rapid apoptosis than wild-type (wt) cells (11Ménissier de Murcia J. Niedergang C. Trucco C. Ricoul M. Dutrillaux B. Mark M. Oliver F.J. Masson M. Dierich A. LeMeur M. Walztinger C. Chambon P. de Murcia G. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 7303-7307Crossref PubMed Scopus (968) Google Scholar). In the present report, we have studied the specificity of the response to different inducers of apoptosis of PARP null cells and the biological meaning of PARP cleavage during apoptosis. To that purpose, we generated a mutant of PARP in which the specific caspase-3 cleavage site 211DEVD214 has been mutated. A fully active, nuclear, and uncleavable protein has been produced and when expressed in PARP−/− cells delays loss of cell viability and the morphological changes associated with apoptosis upon activation of the CD95 receptor. Immortalized mouse embryonic fibroblasts (MEFs) from either PARP+/+ or PARP−/− mice were cultured at 37 °C (5% CO2) in Dulbecco's modified Eagle's medium containing 10% fetal bovine serum, 0.5% gentamicin (Sigma), 4.5 g/liter glucose. Bone marrow cells were isolated and maintained in the same culture medium (Dulbecco's modified Eagle's medium with 4.5 mg/ml glucose) containing 10 ng/ml recombinant interleukin-3 (IL-3). The BS(−) SHT construct bearing the full-length human PARP sequence (14Giner H. Simonin F. de Murcia G. Ménissier-de Murcia J. Gene (Amst.). 1992; 114: 279-283Crossref PubMed Scopus (60) Google Scholar) was used to generate the mutation D214A. The sequence of the oligonucleotide is 5′-GCCACTTCATCCACGCCGGCCACCTCATCGC-3′. The new restriction site NaeI (underlined) generated allowed us to verify the presence of the mutation in further subcloning. Oligonucleotide-directed mutagenesis was performed essentially according to the Amersham kit. After mutagenesis, cDNA was sequenced by the dideoxynucleotide chain termination method. The mutant sequence was recloned in the prokaryotic expression vector pTG 161 PARP, which expressed the wt PARP (15Simonin F. Poch O. Delarue M. de Murcia G. J. Biol. Chem. 1993; 268: 8529-8535Abstract Full Text PDF PubMed Google Scholar) by replacing theBssHII-NcoI wt fragment by the mutated one resulting in pTG 161 D214A-PARP. These vectors were used directly for transformation of the Escherichia coli TGE 900 strain (16Courtney M. Jallat S. Tessier L.H. Benavente A. Crystal R.G. Lecocq J.P. Nature. 1985; 313: 149-151Crossref PubMed Scopus (93) Google Scholar). A fragment PstI-PstI containing the whole cDNA from the PARP and D214A-PARP was introduced into theXhoI site of the eucaryotic expression vector pECV (17Belt P.B. Groeneveld H. Teubel W.J. Van der Putte P. Backendorf C. Gene (Amst.). 1989; 84: 407-417Crossref PubMed Scopus (55) Google Scholar) withPstI-XhoI adapters resulting either in pECV PARP or pECV D214A-PARP, respectively. This was done essentially as described by Schreiber et al. (18Schreiber V. de Murcia G. Ménissier-de Murcia J. Médecine/Sciences. 1992; 8: 134-139Crossref Scopus (3) Google Scholar). Briefly, cells grown on coverslips were washed three times with PBS and fixed with methanol/acetone (v/v) for 10 min at 4 °C. After washing three times with PBS supplemented with Tween 0.1% (v/v), cells were incubated overnight at 4 °C with polyclonal anti-PARP antibody (1:100 dilution). After washing, the coverslips were incubated with a secondary antibody (Texas Red-conjugated) for 4 h at room temperature. Immunofluorescence was evaluated using a Zeiss Axioplan microscope equipped with a wt PARP and D214A-PARP were by in using the with BS(−) PARP, and BS(−) D214A-PARP. In PARP D214A-PARP of a of the were incubated with of caspase-3 from at different times at 37 °C in a containing 10 and 10 These were from PARP−/− splenocytes with during h reported S. J.C. J. 1995; PubMed Scopus Google Scholar). The the in PARP and D214A-PARP of of the of mg/ml and 4 of the 10 10 and of PARP was as described V. M. Ménissier-de Murcia M. de Murcia G. 1997; PubMed Scopus Google Scholar). to of wild-type or mutant PARP proteins were incubated for 10 min at °C in of 4 DNA, NAD+, and The was by of of 10% and the was in a C. H. P. J. Biochem. PubMed Scopus Google Scholar). were by with of vector V. de Murcia G. Ménissier-de Murcia J. Gene (Amst.). 1994; PubMed Scopus Google Scholar) and of wt PARP, D214A-PARP, or the vector were induced to apoptosis by anti-CD95 or h were fixed with in PBS for 10 min at 4 °C and with X-gal, and in PBS for After the number of and cells was cells treatment were as a of cells E. L. M. J. 1997; PubMed Scopus Google Scholar). of the nuclear of apoptosis, were in and by the of a for the green fluorescence protein and 10 of pECV PARP, or were were with anti-CD95 h of apoptotic was performed according to et al. M.D. J.C. Raff M.C. Nature. 1993; PubMed Scopus Google Scholar). Briefly, the cells were fixed in for 10 min at room incubated for 10 min with at and with in PBS containing A for min at 37 °C. The cells were with and with a Zeiss fluorescence bone marrow cells were with for and incubated in were at different times and with for min at 4 °C. at cell and The was with (v/v), and the phase was with and on bone marrow cells are a to biochemical leading to apoptosis by growth removal G. M. A. J. 9: PubMed Scopus Google Scholar). cells were isolated from PARP+/+ and PARP−/− mice (11Ménissier de Murcia J. Niedergang C. Trucco C. Ricoul M. Dutrillaux B. Mark M. Oliver F.J. Masson M. Dierich A. LeMeur M. Walztinger C. Chambon P. de Murcia G. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 7303-7307Crossref PubMed Scopus (968) Google Scholar) and maintained in culture in the presence of inducers of apoptosis, the genotoxic agent MNU, which activates the catalytic of PARP, the topoisomerase I inhibitor a and the removal of have been DNA induced by activates the base excision repair pathway the genotoxic effect produced by CPT-11 not this the apoptosis is of DNA and of from the N. A. M. J. 1996; PubMed Scopus Google Scholar). We have compared the of cells of to these inducers of apoptosis by of DNA into shown in primary cultured bone marrow cells exposed to apoptosis much more than their In PARP−/− cells an increased sensitivity to as by a effect on cell we induced DNA by not base excision we a effect on DNA of the cell when the cells were of there were no significant in the appearance of DNA These cells were sensitive to the induced by activation of the CD95 and in the presence of results have been described using primary Z.-Q. Stingl L. Morrison C. Jantsch M. Marek L. Schulze-Ostoff K. Wagner E. Genes Dev. 1997; 18: 2347-2358Crossref Scopus (517) Google Scholar) or M. Single B. Künstle G. Volbracht C. Hentze H. Nicotera P. Biochem. Biophys. Res. Commun. 1997; 233: 518-522Crossref PubMed Scopus (135) Google Scholar) from PARP null that the presence of PARP is not an for completion of apoptosis. In a more on the role of during apoptosis, that the absence of PARP the cells to cell death CD95 treatment C.M. S. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). This from the of of PARP−/− in the which the to these results that PARP-deficient cells have a apoptotic when the is a agent the such as the alkylating agent apoptosis PARP is cleaved to of and of the fragment that cleavage occurs and Y.A. Kaufmann S.H. Desnoyers S. Poirier G.G. Earnshaw W.C. Nature. 1994; 371: 346-347Crossref PubMed Scopus (2351) Google Scholar) the nuclear of PARP (18Schreiber V. de Murcia G. Ménissier-de Murcia J. Médecine/Sciences. 1992; 8: 134-139Crossref Scopus (3) Google leading to a loss of it has been that the is the for and (4Nicholson D. Thornberry N. Trends Biochem. Sci. 1997; 22: 299-306Abstract Full Text PDF PubMed Scopus (2187) Google Scholar). To further the biological consequences of PARP cleavage on apoptosis, the at was to an in the caspase-3 cleavage to the mutant D214A-PARP the mutation in the nuclear the of the mutated protein was this purpose, PARP−/− cells were with D214A-PARP and the expressed protein was using a polyclonal antibody the whole protein. We that D214A-PARP protein was nuclear, that the is not involved in the nuclear of PARP cells with D214A-PARP cDNA were for poly(ADP-ribose) treatment with as by using an antibody not The same specific was for wt PARP and D214A-PARP in V. M. Ménissier-de Murcia M. de Murcia G. 1997; PubMed Scopus Google Scholar) that the mutation in the NH2-terminal of PARP not the catalytic of the protein as C. E. S. de Murcia G. Ménissier-de Murcia J. 1996; PubMed Scopus Google Scholar). the mutation to a protein was by an in cleavage using human caspase-3 and the PARP by in PARP with caspase-3 in the cleavage of the PARP into the to that during apoptosis. the mutant D214A-PARP with caspase-3 mutant D214A-PARP was to the cleavage by a from PARP−/− splenocytes induced to apoptosis by treatment with MNU, which is a of apoptosis in these cells (11Ménissier de Murcia J. Niedergang C. Trucco C. Ricoul M. Dutrillaux B. Mark M. Oliver F.J. Masson M. Dierich A. LeMeur M. Walztinger C. Chambon P. de Murcia G. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 7303-7307Crossref PubMed Scopus (968) Google that mutation the cleavage by caspase-3 and during apoptosis. PARP has been shown to be an important for caspase-3 M. K. Desnoyers S. Poirier G.G. Cell. 1995; Full Text PDF PubMed Scopus Google activation of which is for apoptosis V. G. J. 1997; Scopus Google Scholar). CD95 is a cell that to the family N. S. A. M. S. M. A. S. Cell. Full Text PDF PubMed Scopus Google Scholar) in Ref. S. Cell. 1997; 88: Full Text Full Text PDF PubMed Scopus Google Scholar). the CD95 by either or by the CD95 ligand apoptosis. CD95 is directly to which and activates a responsible for the execution phase of apoptosis (4Nicholson D. Thornberry N. Trends Biochem. Sci. 1997; 22: 299-306Abstract Full Text PDF PubMed Scopus (2187) Google Scholar). the upon activation of caspase-3 by PARP protein is L. Thornberry A. J. 1996; PubMed Scopus Google Scholar). PARP cleavage a of programmed cell To the presence of an uncleavable PARP mutant is during the to apoptosis, we have different to induce apoptosis in treatment of the cells with either a CD95 of DNA or with the alkylating agent MMS, to DNA are by and PARP PARP−/− were with the with the vectors the wt PARP or the D214A-PARP mutant or the Apoptosis was in cells either an anti-CD95 treatment or to an alkylating A shows that h anti-CD95 treatment cells were of wt PARP not to cell However, cells the uncleavable PARP mutant a significant delay of 10 h in the loss of cell viability, that PARP cleavage is for the cell to the apoptotic in To that loss of cell viability was of activation of apoptosis, a specific inhibitor of A. Thornberry J.P. M. M. Y.A. Nature. 1995; PubMed Scopus Google was of cells with this inhibitor at cell death B) as has been shown V. G. J. 1997; Scopus Google Scholar). In PARP null cells are more sensitive to apoptosis induced by a monofunctional alkylating agent, and the of wt PARP the viability of PARP−/− cells that the absence of PARP is directly responsible for the of cells to DNA with the D214A-PARP mutant are the of and the sensitivity of PARP−/− cells to the same as wt PARP in this the absence of PARP cleavage not to the of cell To at which the of PARP with the apoptotic we have the of apoptotic PARP−/− cells during anti-CD95 this purpose, were with vectors the wt or the uncleavable PARP and a the green fluorescence protein as described and We established three different of cells GFP, according to the of the and cells 4 cells with but 4 and cells with a 4 the cells in the had the membrane according to morphological In wt PARP, were cells, and apoptotic cells had the nuclear 4 In cells the D214A-PARP mutant were much more to were cells, and the of apoptotic cells with nuclear was compared with their In conclusion, the of PARP not the nuclear of apoptosis but with the leading to cell membrane blebbing, as by the number of cells at this from different have the role of PARP in the apoptotic We have shown that splenocytes isolated from PARP−/− mice programmed cell death much more than their when with an alkylating agent (11Ménissier de Murcia J. Niedergang C. Trucco C. Ricoul M. Dutrillaux B. Mark M. Oliver F.J. Masson M. Dierich A. LeMeur M. Walztinger C. Chambon P. de Murcia G. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 7303-7307Crossref PubMed Scopus (968) Google Scholar). These with in that PARP−/− cells are sensitive to DNA are by base excision but are sensitive to inducers of apoptosis that not this pathway Z.-Q. Stingl L. Morrison C. Jantsch M. Marek L. Schulze-Ostoff K. Wagner E. Genes Dev. 1997; 18: 2347-2358Crossref Scopus (517) Google Scholar, 13Leist M. Single B. Künstle G. Volbracht C. Hentze H. Nicotera P. Biochem. Biophys. Res. Commun. 1997; 233: 518-522Crossref PubMed Scopus (135) Google Scholar). To this specific we have to into that PARP in the pathway in with DNA polymerase and K. S. P. S. Res. 1996; PubMed Scopus Google Scholar, F. de Murcia G. Ménissier-de Murcia J. Res. Scopus Google Scholar, M. Niedergang C. Schreiber V. S. Ménissier-de Murcia J. de Murcia G. Mol. Cell. Biol. 18: PubMed Scopus Google Scholar) and in the organization of chromatin architecture the of Murcia G. A. Poirier G.G. Biochem. Biol. Google Scholar, A. de Murcia G. S. M. L. D. Poirier G.G. J. Biol. Chem. 1989; Full Text PDF PubMed Google Scholar). The reason these cells lacking PARP are much more and programmed cell death than cells be by the of DNA of the absence of which the cell to and the apoptotic pathway to of DNA to a new of cells. This is by the that PARP−/− cells have of DNA as by the C. Oliver F.J. N. V. de Murcia G. Ménissier-de Murcia J. Res. PubMed Scopus Google Scholar) and an increased of in PARP null splenocytes (11Ménissier de Murcia J. Niedergang C. Trucco C. Ricoul M. Dutrillaux B. Mark M. Oliver F.J. Masson M. Dierich A. LeMeur M. Walztinger C. Chambon P. de Murcia G. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 7303-7307Crossref PubMed Scopus (968) Google Scholar) upon treatment with an alkylating A biochemical of apoptosis is the proteolytic cleavage and of PARP in the execution phase of cell in apoptosis is by of PARP cleavage is to is the cell to of this protein to apoptosis. of chromatin is a key of the apoptotic process. DNA during apoptosis is produced by in the of chromatin M. C. J. Res. 1993; PubMed Scopus Google and PARP with DNA breaks E. F. Ménissier-de Murcia J. J.A. A. V. B. E. de Murcia G. J. Mol. Biol. 1994; PubMed Scopus Google Scholar). this PARP facilitates the and of the proteins to repair of PARP by apoptotic to a disable key of the genomic with L. Thornberry A. J. 1996; PubMed Scopus Google to DNA repair during chromatin and the of to chromatin and nuclear In of it has been shown that of PARP by to the cells results in an increased of to chromatin M. Res. 1994; Google Scholar). The of PARP in the of the nuclear F. de Murcia G. Ménissier-de Murcia J. Res. Scopus Google Scholar) that its cleavage during apoptosis in nuclear disassembly and facilitates which are retarded upon expression of the uncleavable PARP In the uncleavable PARP mutant for the of PARP which cell viability upon anti-CD95 stimulation. The morphological consequences of uncleavable of on apoptosis have been for lamin L. D. E. J. Biol. 1996; PubMed Scopus Google Scholar) and 1997; PubMed Scopus Google Scholar). Mutant cells no of chromatin or nuclear shrinkage and during apoptosis membrane cell blebbing, the nuclear were of PARP cleavage has consequences at the and nuclear We have in a delay in cell and in chromatin in cells D214A-PARP anti-CD95 These on cell are to of proteases with specific These of the apoptotic such as the of and nuclear but not of cell N. M. C. G. J. Biol. 1997; PubMed Scopus Google Scholar). PARP cleavage is not to apoptosis as and cell PARP cleavage loss of cell viability proteolytic of cell leading to cell This of apoptosis upon uncleavable PARP PARP as a key targeted for early in the apoptotic process. In the results in this that PARP is not a but plays a role the cell not to apoptosis when the cell is to repair the cleavage be a that the cell is to with a DNA from either chromatin or an genotoxic We are to E. for to for the of to for and to for critical of the